Ferric carboxylmethyl konjacglucomannan gel microspheres (CMKGM-Fe) were prepared by cross-linking carboxyl methyl konjac glucomannan (CMKGM) with ferric ions (Fe3+). The complex of CMKGM-Fe/benzoic acid was characterized by IR spectroscopy. The adsorption capacity of CMKGM-Fe for benzoic acid was studied by UV-vis spectroscopy. Several parameter's including the adsorption time, temperature, microsphere size, and the concentrations of CMKGM, FeCl3, and benzoic acid were investigated. The results showed that adsorption equilibrium could be established in about 11 h. When the temperature was 298 K, the CMKGM concentration was 1.5 % (w/v), the mass ratio of Fe3+ was 2.5 % (w/v), and the initial concentration of benzoic acid was 1000 mg.L-1 and the adsorption capacity attained 0.4954 mmol.g(-1). According to the adsorption isotherms of benzoic acid on CMKGM-Fe, the thermodynamic parameters of adsorption process were calculated. The experimental data were fitted with the Freundlich equation, and it was found that the equation was suitable for the study of the investigated adsorption system. The entropy value of the system is negative, and cooling is beneficial for the adsorption, suggesting that the system is a spontaneous exothermic process.